This article addresses, from a Frankfurt School perspective on law identified with Franz Neumann and more recently Habermas, the attack upon the principles of war criminality formulated at the Nuremberg trials by the increasingly influential legal and political theory of Carl Schmitt. It also considers the contradictions within certain of the defence arguments that Schmitt himself resorted to when interrogated as a possible war crimes defendant at Nuremberg. The overall argument is that a distinctly internal, or “immanent”, form of critique is required of Schmitt's position, in which its is found wanting even on its own terms. In principle, the application of this dialectical mode of critique can allow a genuine debate to emerge between those seeking to continue both the Schmittian and critical theory traditions, whilst safeguarding the latter from the dangers of formulating polemical interventions that are, in effect, counterproductive to their own intentions.